Several prosthetic joints have been proposed for various extremity joints, such as the joints in the hands and feet. For example, U.S. Pat. No. 5,984,970 shows prosthetic joints that may be used in both the distal interphalangeal joints and the proximal interphalangeal joint. Among the desirable qualities of such a prosthetic joint is the ability to provide natural flexion motion and durability. The interphalangeal joints ideally permit at least between 70° and 90° of flexion (i.e. bending the finger or toe in the normal direction) and at least a small amount of hyperextension, (i.e. bending of the finger or toe backwards).
Typically, prosthetic extremity joints, particularly interphalangeal or metacarpophalangeal, are used to replace natural joints compromised by degenerative or inflammatory joint disease, dislocation of the joints, or other painful joints having limitation of motions. Adequate bone stock and lack of infection are typically also required.
Prior art proximal interphalangeal joint prosthetics typically employ two intramedullary stems or arms with a pivoting unit located therebetween. In some devices, the entire prosthetic is formed of a single piece of elastomer. The pivoting unit includes a dorsal concavity and in some cases a small palmar concavity. The concavities provide a “weak” spot that encourages the location of the pivoting deformation to the hinge, thereby producing predictable and natural motion. One drawback to many of these devices is that they employ no angle between the opposing stems in their natural position (i.e. without force applied). Such a position is unnatural as the natural “at-rest” posture of the phalanges is not a straight line.
One product, the Avanta PIP offered by Avanta Orthopedics, addresses this drawback by providing a proximal interphalangeal prosthetic that includes stems that are designed to accommodate the crescent shape of the distal and proximal phalanges.
One drawback to many prior art devices, including the Avanta PIP device, is the potential for failure at the pivot or hinge portion of the implant. Such failures require intervention and, as a result, are extremely undesirable. Some devices used for other joints may be larger and thus less prone to failure, but such devices may not be suitable for small joints such as interphalangeal joints.
Accordingly, there is a need for a prosthetic joint component that is less prone to joint failure than existing joint devices. There is a further need for such a prosthetic joint component that is particularly suited to the limitations of the interphalangeal joints.